Janeway says James T. Kirk claimed to have met Leonardo Da Vinci. This happened in Requiem for Methuselah (1969) when Kirk, Spock, and McCoy met a man named Flint, a 5000-year-old man from Earth, who claimed to have assumed the identity of many different artists throughout Earth's history, including Leonardo.
Tuvok wears the same costume that was worn by the mirror universe Tuvok in Through the Looking Glass (1995).
Although Captain Janeway visits the Leonardo program several other times, the only times Leonardo himself appears are in Scorpion (1997) (opening scene only) and this one "Concerning Flight."
The piece of "technology" Leonardo holds in his hand (about 12 mins) is actually part of a car alternator which was also used as the drug dispensing unit in Star Trek The Next Generation "Symbiosis".
During the final scene, the closed captions (in some presentations) for this episode contain an additional, unspoken line of dialogue between Janeway and Leonardo. He asks if Janeway can speak French and suggests he may have use for an assistant in Paris, potentially changing the tone of the scene.